1. Field of the Invention
The present invention relates to a bicycle seat post structure, and more particularly to a structure that the bicycle seat cannot be adjusted either up or down when the seat height is set.
2. Background of the Invention
A bicycle seat post is mounted to the bottom of the seat for supporting the seat so as to be fixed to the bicycle frame. The bicycle seat post has a top end fastened to the bottom of the seat and a bottom end inserted into and secured to the seat tube of the bicycle frame. The bicycle seat post is generally disposed with mechanical adjustment mechanisms or oil hydraulic adjustment mechanisms; the bicycle seat post with mechanical adjustment mechanisms employs mechanical mechanisms to control the relative position of the inner and the outer tubes of the seat post so as to adjust the seat height; the bicycle seat post with oil hydraulic adjustment mechanisms employs the hydraulic force from hydraulic members to control the relative position of the inner and the outer tubes of the seat post so as to adjust the seat height. As disclosed in Taiwan Patent Application No. 089221346, No. 097206782, and No. 099137166, those cases provide the aforesaid bicycle seat post with oil hydraulic adjustment mechanisms. A prior art bicycle seat post with oil hydraulic adjustment mechanisms is provided with an actuator inside the seat post. The actuator includes a cylinder barrel that is arranged with a floating piston and an axial displacement valve driven by a pin, and wherein the cylinder barrel is provided with an upper oil compartment between the floating piston and the axial displacement valve, a lower oil compartment under the axial displacement valve, and an air compartment above the floating piston. When the prior art bicycle seat post with oil hydraulic adjustment mechanisms is in use and the height thereof is set and further it is locked by a pin, the oil within the upper and the lower oil compartments stops flowing and the lower oil compartment is filled with oil so as to cause the seat to stop moving down and to be fixed. In addition, the air compartment is arranged above the floating piston; when the user pulls the seat upward, consequently, the pin and the valve compresses the air within the air compartment and they simultaneously move upward with the seat, so that a sliding space between the bicycle seat and the bicycle frame is produced when the user lifts the bicycle by holding onto the seat of the bicycle. Thus, it doesn't seem to the user that the bicycle seat is combined with the bicycle frame as a whole because the bicycle seat seems disconnected from the bicycle frame in the beginning when the bicycle is lifted by holding onto the bicycle seat. It is against this background and the problems associated therewith that the present invention has been developed.